[!123] Use files in CMake <-> Python interface instead of stdout
Merge branch 'feature/avoid-stdout-in-python-cmake-interface' into 'master' ref:quality/dune-testtools stdout may always be cluttered with warnings etc. and is not a robust tool in interfacing information into CMake. This fixes [#134] See merge request [!123] [#134]: gitlab.dune-project.org/NoneNone/issues/134 [!123]: gitlab.dune-project.org/quality/dune-testtools/merge_requests/123 Closes #134